Trimetallic reforming catalyst

ABSTRACT

An improved reforming process utilizing a novel trimetallic catalytic composite is disclosed. The composite comprises a refractory support having a nominal diameter of at least 650 microns and having deposited thereon a uniformly dispersed platinum component, a uniformly dispersed Group IVA metal component and a surface-impregnated metal component selected from the group consisting of rhdoium, ruthenium, cobalt, nickel, or iridium. When this catalytic composite is used in the reforming of hydrocarbons at low pressures, significant improvements in activity and stability are observed compared to catalysts of the prior art.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional application of prior copending application Ser. No.065,541 filed June 23, 1987, now U.S. Pat. No. 4,791,087 which in turnis a continuation-in-part of application Ser. No. 910,099 filed Sept.22, 1986, now U.S. Pat. No. 4,677,094, the contents of which areincorporated herein by reference thereto.

BACKGROUND OF THE INVENTION

The subject of the present invention is an improved hydrocarbonconversion process employing a novel catalytic composite. Morespecifically, the present invention involves an improved reformingprocess employing a novel dual-function trimetallic catalytic compositehaving both a hydrogenation-dehydrogenation function and a crackingfunction which quite surprisingly, shows exceptional activity andresistance to deactivation.

Composites having a hydrogenation-dehydrogenation function and acracking function are widely used today as catalysts in many industriessuch as the petroleum and petrochemical industry to accelerate a widespectrum of hydrocarbon conversion reactions. Generally, the crackingfunction is thought to be associated with an acid-acting material of theporous, adsorptive, refractory oxide type which is typically utilized asthe support or carrier for a heavy metal component such as the metals orcompounds of metals of Groups V through VIII of the Periodic Table towhich are generally attributed the hydrogenation-dehydrogenationfunction.

These catalytic composites are used to accelerate a wide variety ofhydrocarbon conversion reactions such as hydrocracking, isomerization,dehydrogenation, hydrogenation, desulfurization, cyclization,alkylation, polymerization, cracking, hydroisomerization, etc. In manycases, the commercial applications of these catalysts are in processeswhere more than one of these reactions are proceeding simultaneously.The present example of this type of process is reforming, wherein ahydrocarbon feed stream containing paraffins and naphthenes is subjectedto conditions which promote dehydrogenation of naphthenes to aromatics,dehydrocyclization of paraffins to aromatics, isomerization of paraffinsand naphthenes, hydrocracking of naphthenes and paraffins and the likereactions to produce an octane-rich or aromatic-rich product stream.Another example is a hydrocracking process wherein catalysts of thistype are utilized to effect selective hydrogenation and cracking of highmolecular weight unsaturated materials, selective hydrocracking of highmolecular weight materials, and other like reactions, to produce agenerally lower boiling, more valuable output stream. Yet anotherexample is an isomerization process wherein a hydrocarbon fraction whichis relatively rich in straight-chain paraffin compounds is contactedwith a dual-function catalyst to produce an output stream rich inisoparaffin compounds.

It is of critical importance that the dual-function catalysts exhibitnot only the capability to initially perform its specified functions,but also that it has the capability to perform them satisfactorily forprolonged periods of time. The analytical terms used in the art tomeasure how well a particular catalyst performs its intended functionsin a particular hydrocarbon reaction environment are activity,selectivity and stability. And for purposes of discussion here, theseterms are conveniently defined for a given charge stock as follows: (1)activity is a measure of the catalyst's ability to convert hydrocarbonreactants into products at a specified severity level where severitylevel means the specific reaction conditions used--that is, thetemperature, pressure, contact time, and presence of diluents such as H₂; (2) selectivity refers to the amount of desired product or productsobtained relative to the amount of reactants charged or converted, (3)stability refers to the rate of change with time of the activity andselectivity parameters--obviously, the smaller rate implying the morestable catalyst. In a reforming process, activity commonly refers to theamount of conversion that take place for a given charge stock at aspecified severity level and is typically measured by octane number ofthe C₅ ⁺ product stream, selectivity refers to the amount of C₅ ⁺ yieldthat is obtained at a particular activity level; and stability istypically equated to the rate of change with time of activity, asmeasured by octane number of C₅ ⁺ product, and of selectivity, asmeasured by C₅ ⁺ yield. Actually, the last statement is not strictlycorrect because generally a continuous reforming process is run toproduce a constant octane C₅ ⁺ product with severity level beingcontinuously adjusted to attain this result; and, furthermore, theseverity level is for this process usually varied by adjusting theconversion temperature in the reaction zone so that, in point of fact,the rate of change of activity finds response in the rate of change ofconversion temperature and changes in this last parameter arecustomarily taken as indicative of activity stability.

As is well known to those skilled in the art, the principal cause ofobserved deactivation or instability of a dual-function catalyst when itis used in a reforming process is associated with the fact that cokeforms on the surface of the catalyst during the course of the reaction.More specifically, the conditions utilized typically result in theformation of heavy, high molecular weight, black, solid or semi-solid,carbonaceous material which coats the surface of the catalyst andreduces its activity by shielding its active sites from the reactants.In other words, the performance of this dual-function catalyst issensitive to the presence of carbonaceous deposits on the surface of thecatalyst. Accordingly, the major problem facing workers in this area ofthe art is the development of more active and selective catalyticcomposites that are not as sensitive to the presence of thesecarbonaceous materials and/or have the capability to suppress the rateof the formation of these carbonaceous materials on the catalyst. Thissensitivity to formation of carbonaceous materials is amplified aspractitioners of the art reduce pressure and increase the severity ofprocessing units in an attempt to extract the maximum octane-barrelsfrom a given feedstock. Viewed in terms of performance parameters, theproblem is to develop a dualfunction catalyst having superior activity,selectivity and stability while operating at pressures less than 862kPa(ga).

OBJECTS AND EMBODIMENTS

Accordingly, it is an object of the present invention to provide animproved catalytic reforming process for improving the anti-knockproperties of a gasoline fraction. A corollary objective is to providean improved catalyst for the reforming of hydrocarbons.

In its broadest embodiment, the invention involves a process for thecatalytic reforming of a naphtha charge stock to produce a high-octanereformate comprising contacting the naphtha and hydrogen at reformingconditions with a catalytic composite comprising a uniformly dispersedplatinum component, a uniformly dispersed Group IVA metal component, asurface-impregnated metal component selected from the group consistingof rhodium, ruthenium, cobalt, nickel or iridium and a halogen componenton a refractory support having uniform composition and a nominaldiameter of at least about 650 microns.

In an alternate embodiment, the present invention is a catalyticcomposite for the conversion of hydrocarbons comprising a uniformlydispersed platinum component, a uniformly dispersed Group IVA metalcomponent, a surface-impregnated metal component selected from the groupconsisting of rhodium, ruthenium, cobalt, nickel, or iridium, and ahalogen component on a refractory support having a uniform compositionand a nominal diameter of at least about 650 microns.

These as well as other objects and embodiments will become apparent uponreview of the more detailed description of the invention hereinafter setforth.

INFORMATION DISCLOSURE

Several catalytic composites relevant to the composition of the instantinvention are disclosed in the art. However, no reference or combinationof references discloses the unique combination of components of theinstant invention.

U.S. Pat. No. 3,651,167 (deRosset) discloses a catalyst composition forthe selective hydrogenation of C₄ -acetylenes utilizing a catalystcomprising a Group VII noble metal, preferably palladium, deposited on arefractory inorganic oxide carrier material wherein said Group VII noblemetal is surfaceimpregnated. This reference is totally silent to theadvantageous use of a surface-impregnated metal in combination withuniformly dispersed platinum and Group IVA metal. Further, it ispreferred in this reference that the catalyst be non-acidic, which is incontradistinction to the instant invention where it is essential that ahalogen component be included in the catalyst composition.

U.S. Pat. No. 3,840,471 (Acres) discloses a catalytic compositioncontaining platinum, rhodium, and a base metal composited on an inertmaterial wherein a Group IVA metal may be chosen as one of a possible 25base metals disclosed. The intended use of this catalyst is for theoxidation reaction of organic compounds, specifically the oxidation ofengine or combustion exhausts. Further, this reference is not evenremotely cognizant of the beneficial effect of surface-impregnatedrhodium.

Of particular interest is the catalyst disclosed in U.S. Pat. No.3,898,154 (Rausch). This reference discloses a catalytic compositecomprising platinum, rhodium, tin, and a halogen or a porous carriermaterial. The reference, however, teaches that it is an essentialfeature that the rhodium component may be incorporated by any meansknown to result in a uniform dispersion thereof in the carrier material.A similar reference, U.S. Pat. No. 3,909,394 (Rausch), discloses acatalytic composite comprising platinum, ruthenium, and a halogen on aporous support. Additionally, it is disclosed that the catalyst maycomprise a Group IVA metallic component, with a tin component beingspecifically disclosed as one of the possible constituents. Thisreference, however, teaches that it is an essential feature that thecomponents thereof are uniformly distributed throughout the porouscarrier material. In particular, it is taught in the reference that theruthenium component may be incorporated by any means known to result ina uniform dispersion thereof in the carrier material. Accordingly, itcan be seen that the reference contemplates the use of ruthenium,platinum, tin, and halogen with a porous support, but with the rutheniumuniformly distributed. By way of contrast, it has been discovered in thepresent invention that an improved catalyst is obtained when a metalcomponent selected from the group consisting of rhodium, ruthenium,cobalt, nickel, or iridium is nonuniformly dispersed, i.e.,surface-impregnated. Further, as the surprising and unexpected resultsof the examples presented hereinafter show, a catalyst with asurface-impregnated metal component demonstrates superior performancewhen compared to a prior art catalyst having the same metal uniformlydispersed.

DETAILED DESCRIPTION OF THE INVENTION

To reiterate briefly, in its broadest embodiment, the present inventionis a process for the catalytic reforming of a naphtha charge stockcomprising contacting the naphtha and hydrogen at reforming conditionswith a catalytic composite comprising a uniformly dispersed platinumcomponent, a uniformly dispersed Group IVA metal component, asurface-impregnated metal component selected from the group consistingof rhodium, ruthenium, cobalt, nickel, or iridium, and a halogencomponent on a refractory support having a nominal diameter of at leastabout 650 microns.

According to the present invention, a hydrocarbon charge stock andhydrogen are contacted with the trimetallic catalyst described above ina reforming operation. This contacting may be accomplished by using thecatalyst in a fixed bed system, a moving bed system, a fluidized bedsystem, or in a batch type operation. In the fixed bed system, ahydrogen-rich gas and the charge stock are preheated by any suitableheating means to the desired reaction temperature and then are passedinto a conversion zone containing a fixed bed of the catalyst typepreviously characterized. It is, of course, understood that theconversion zone may be one or more separate reactors with suitable meanstherebetween to ensure that the desired conversion temperature ismaintained at the entrance to each reactor. It is also important to notethat the reactants may be contacted with the catalyst bed in eitherupward, downward, or radial flow fashion with the latter beingpreferred. In addition, the reactants may be in the liquid phase, amixed liquid-vapor phase, or a vapor phase when they contact thecatalyst, with best results obtained in the vapor phase.

The reforming system will comprise a reforming zone containing a fixedor moving bed of the catalyst types previously characterized. Thisreforming zone may be one or more separate reactors with suitableheating means therebetween to compensate for the endothermic nature ofthe reactions that take place in each catalyst bed. The hydrocarbon feedstream that is charged to this reforming system will comprisehydrocarbon fractions containing naphthenes and paraffins that boilwithin the gasoline range. The preferred charge stocks are naphthas,those consisting essentially of naphthenes and paraffins, although inmany cases aromatics will also be present. This preferred class includesstraight run gasolines, natural gasolines, synthetic gasolines, and thelike. On the other hand, it is frequently advantageous to chargethermally or catalytically cracked gasolines or higher boiling fractionsthereof. Mixtures of straight run and cracked gasoline range naphthacharge stock may be a full boiling gasoline having an initial boilingpoint of from about 10° to about 66° C. and an end boiling point withinthe range of from about 163° to about 218° C., or may be a selectedfraction thereof which generally will be a higher boiling fractioncommonly referred to as a heavy naphtha--for example, a naphtha boilingin the range of C₇ to 204° C. In some cases, it is also advantageous tocharge pure hydrocarbons or mixtures of hydrocarbons that have beenextracted from hydrocarbon distillates--for example, straight-chainparaffins--which are to be converted to aromatics. It is preferred thatthese charge stocks be treated by conventional catalytic pretreatmentmethods such as hydrorefining, hydrotreating, hydrodesulfurization,etc., to remove substantially all sulfurous, nitrogenous andwater-yielding contaminants therefrom, and to saturate any olefins thatmay be contained therein.

In a reforming embodiment, it is generally a preferred practice to usethe present catalytic composite in a substantially water-freeenvironment. Essential to the achievement of this condition in thereforming zone is the control of the amount of water and water-producingcompounds present in the charge stock and the hydrogen stream which arebeing charged to the zone. Best results are ordinarily obtained when thetotal amount of water entering the conversion zone from any source isheld to a level substantially less than 50 ppm, and preferably less than20 ppm, expressed as weight of equivalent water in the charge stock. Ingeneral, this can be accomplished by an appropriate pretreatment of thecharge stock coupled with the careful control of the water present inthe charge stock and in the hydrogen stream; the charge stock can bedried by using any suitable drying means known to the art such as aconventional solid adsorbent having a high selectivity for water, forinstance, sodium or calcium crystalline aluminosilicates, silica, gel,activated alumina, molecular sieves, anhydrous calcium sulfate, highsurface area sodium and the like adsorbents. Similarly, the watercontent of the charge stock may be adjusted by suitable strippingoperations in a fractionation column or like device. An in some cases, acombination of adsorbent drying and distillation drying may be usedadvantageously to effect almost complete removal of water from thecharge stock. Preferably, the charge stock is dried to a levelcorresponding to less than 20 ppm of H₂ O equivalent. In general, it ispreferred to control the water content of the hydrogen stream enteringthe hydrocarbon conversion zone within a level of about 5 to 20 vol. ppmof water or less.

An effluent stream is withdrawn from the reforming zone and passedthrough a cooling means to a separation zone, typcally maintained atabout -4° to 66° C., wherein a hydrogen-rich gas is separated from ahigh octane liquid product, commonly called an "unstabilized" reformate.When the water content of the hydrogen-rich gas is greater than desired,a portion of this hydrogen-rich gas is withdrawn from the separatingzone and passed through an adsorption zone containing an adsorbentselective for water. The resultant substantially water-free hydrogenstream is then recycled through suitable compressing means back to thereforming zone. If the water content of the hydrogen-rich gas is withinthe range specified, then a substantial portion of it can be directlyrecycled to the reforming zone, the liquid phase from the separatingzone is typically withdrawn and commonly treated in a fractionatingsystem in order to adjust the butane concentration, thereby controllingfront-end volatility of the resulting reformate.

The conditions utilized for the present invention include a pressureselected from the range of about 101 to about 6995 kPa, with thepreferred pressure being about 446 to about 2514 kPa. Particularly goodresults are obtained at low pressure, namely, a pressure of about 446 to791 kPa. In fact, it is a singular advantage of the present inventionthat it allows stable operation at lower pressures than have heretoforebeen successfully utilized in so-called "continuous" reforming systemswith a bimetallic catalyst (i.e., reforming for periods of about 0.5 toabout 5 or more barrels of charge per pound of catalyst withoutregeneration). In other words, the catalyst of the present inventionallows the operation of a continuous reforming system to be conducted atlower pressure, i.e. about 345 kPa (ga), for about the same or bettercatalyst life before regeneration as has been heretofore realized withconventional bimetallic catalysts at higher pressures, i.e. 862 kPa(ga).

Similarly, the temperature required for reforming with the subjectcatalyst is generally lower than that required for a similar reformingoperation using a high quality bimetallic platinum catalyst of the priorart. This significant and desirable feature of the present invention isa consequence of the selectivity of the catalyst of the presentinvention for the octane-upgrading reactions that are preferably inducedin a typical reforming operation. Hence, reforming conditions include atemperature in the range of from about 427° to about 593° C. andpreferably about 482° to about 566° C. As is well known to those skilledin the continuous reforming art, the initial selection of thetemperature within this broad range is made primarily as a function ofthe desired octane of the product reformate considering thecharacteristics of the charge stock and the catalyst. Ordinarily, thetemperature then is thereafter slowly increased during the run tocompensate for the inevitable deactivation that occurs to provide aconstant octane product.

It is a feature of the present invention that the rate at which thetemperature is increased in order to maintain a constant octane productis substantially lower for the catalyst of the present invention.Moreover, for the catalyst of the present invention, the C₅ ⁺ yield lossfor a given temperature increase is substantially lower than for a highquality bimetallic reforming catalyst of the prior art. In addition,hydrogen production is substantially higher.

The reforming conditions of the present invention also includesufficient hydrogen to provide an amount of about 1 to about 20 moles ofhydrogen per mole of hydrocarbon entering the reforming zone, withexcellent results being obtained when about 5 to about 10 moles ofhydrogen are used per mole of hydrocarbon. The liquid hourly spacevelocity (LHSV) included in the reforming conditions employed in theinvention is selected from the range of about 0.1 to about 10 hr⁻ with avalue in the range of about 1 to about 5 hr⁻ 1 being preferred. In fact,the present invention allows operations to be conducted at a higher LHSVthan normally can be stably achieved in a continuous reforming processwith a high quality bimetallic platinum reforming catalyst of the priorart. The last feature is of immense economic significance because itallows a continuous reforming process to operate at the same throughputlevel with less catalyst inventory than that heretofore used withconventional reforming catalysts at no sacrifice in catalyst life beforeregeneration.

Accordingly, considering first the refractory support utilized in thepresent invention, it is preferred that the material be a porous,adsorptive, highsurface area support having a surface area of about 25to about 500 m² /g. The porous carrier material should also be uniformin composition and relatively refractory to the conditions utilized inthe hydrocarbon conversion process. By the term "uniform composition",it is meant that the support be unlayered, has no concentrationgradients of the species inherent to its composition, and is completelyhomogeneous in composition. Thus, if the support is a mixture of two ormore refractory materials, the relative amounts of these materials willbe constant and uniform throughout the entire support. It is intended toinclude within the scope of the present invention carrier materialswhich have traditionally been utilized in dual-function hydrocarbonconversion catalysts such as: (1) activated carbon, coke, or charcoal;(2) silica or silica gel, silicon carbide, clays and silicates includingthose synthetically prepared and naturally occurring, which may or maynot be acid treated, for example, attapulgus clay, diatomaceous earth,fuller's earth, kaolin, kieselguhr, etc.; (3) ceramics, porcelain,bauxite; (4) refractory inorganic oxides such as alumina, titaniumdioxide zirconium dioxide, chromium oxide, zinc oxide, magnesia, thoria,boria, silica-alumina, silica-magnesia, chromia-alumina, alumina-boria,silica-zirconia, etc.; (5) crystalline zeolitic aluminosilicates, suchas naturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; and, (6) combinations of one or moreelements from one or more of these groups. The preferred porous carriermaterials for use in the present invention are refractory inorganicoxides, with best results obtained with an alumina carrier material.Suitable alumina materials are the crystalline aluminas known as thegamma-, eta-, and theta-aluminas, with gamma-alumina giving bestresults. In addition, in some embodiments, the alumina carrier materialmay contain minor proportions of other well known refractory inorganicoxides such as silica, zirconia, magnesia, etc.; however, the preferredsupport is substanitally pure gamma-alumina. Preferred carrier materialshave an apparent bulk density of about 0.3 to about 0.7 g/cc and surfacearea characteristics such that the average pore diameter is about 20 to300 angstroms, the pore volume is about 0.1 to about 1 cc/g. In general,excellent results are typically obtained with a gamma-alumina carriermaterial which is used in the form of spherical particles having arelatively small diameter (i.e., typically about 1/16-inch), an apparentbulk density of about 0.5 g/cc, a pore volume of about 0.4 cc/g, and asurface area of about 175 m² /g.

The preferred alumina carrier material is uniform in composition and maybe prepared in any suitable manner and may be synthetically prepared ornatural occurring. Whatever type of alumina is employed, it may beactivated prior to use by one or more treatments including drying,calcination, steaming, etc., and it may be in a form known as activatedalumina, activated alumina of commerce, porous alumina, alumina gel,etc. For example, the alumina carrier may be prepared by adding asuitable alkaline reagent, such as ammonium hydroxide to a salt ofaluminum such as aluminum chloride, aluminum nitrate, etc., in an amountto form an aluminum hydroxide gel which, upon drying and calcining, isconverted to alumina.

The refractory support may be formed in any desired shape such asspheres, pills, cakes, extrudates, powders, granules, etc. However, itis a feature of the invention that the support be of sufficient sizesuch that it has a nominal diameter of at least about 650 microns. Bythe term "nominal diameter", it is meant the narrowest characteristicdimension. Thus, if the shape of the support is a sphere, the diameterthereof must be at least about 650 microns. Alternatively, if the shapeis an extruded cylinder, the diameter of the circular face must be atleast 650 microns and the length of the cylinder must be at least 650microns. Likewise, if the shape of the catalyst is a cube, the length ofeach side must be at least 650 microns. Typically, the preferred nominaldiameter is within the range of from about 650 to about 3200 microns.Best results are obtained when the support has a diameter of from 1500microns.

For purposes of the present invention, a particularly preferred form ofalumina is the sphere; and alumina spheres may be continuouslymanufactured by the well known oil-drop method which comprises: formingan alumina hydrosol by any of the techniques taught in the art andpreferably by reacting aluminum metal with hydrochloric acid; combiningthe resulting hydrosol with a suitable gelling agent; and dropping theresultant mixture into an oil bath maintained at elevated temperatures.The droplets of the mixture remain in the oil bath until they set andform hydrogel spheres. The spheres are then continuously withdrawn fromthe oil bath and typically subjected to specific aging and dryingtreatments in oil and an ammoniacal solution to further improve theirphysical characteristics. The resulting aged and gelled particles arethen washed and dried at a relatively low temperature of about 149° toabout 204° C. and subjected to a calcination procedure at a temperatureof about 454° to about 704° C. for a period of about 1 to about 20hours. This treatment effects conversion of the alumina hydrogel to thecorresponding crystalline gammaalumina. See the teachings of U.S. Patent2,620,314 for additional details.

One essential ingredient of the subject catalyst is the uniformlydispersed platinum component. This platinum component may exist withinthe final catalytic composite as a compound such as oxide, sulfide,halide, oxyhalide, etc., in chemical combination with one or more of theother ingredients of the composite or as an elemental metal. Bestresults are obtained when substantially all of this component is presentin the elemental state. Generally, this component may be present in thefinal catalyst composite in any amount which is catalytically effectivebut relatively small amounts are preferred. In fact, the platinumcomponent generally will comprise about 0.01 to about 2 wt. % of thefinal catalytic composite, calculated on an elemental basis. Excellentresults are obtained when the catalyst contains about 0.05 to about 1wt. % of platinum.

This platinum component may be incorporated in the catalytic compositein any suitable manner, such as coprecipitation or cogelation,ionexchange, or impregnation, provided that a uniform dispersion of theplatinum component within the carrier material results. The preferredmethod of preparing the catalyst involves the utilization of a soluble,decomposable compound of platinum to impregnate the carrier material.For example, this component may be added to the support by comminglingthe latter with an aqueous solution of chloroplatinic acid. Otherwater-soluble compounds of platinum may be employed in impregnationsolutions and include ammonium chloroplatinate, bromoplatinic acid,platinum dichloride, platinum tetrachloride hydrate, platinumdichlorocarbonyl dichloride, dinitrodiaminoplatinum, etc. Theutilization of a platinum chloride compound, such as chloroplatinc acid,is preferred since it facilitates the incorporation of both the platinumcomponent and at least a minor quantity of the halogen component in asingle step. Best results are obtained in the preferred impregnationstep if the platinum compound yields complex anions containing platinumin acidic aqueous solutions. Hydrogen chloride or the like acid is alsogenerally added to the impregnation solution in order to furtherfacilitate the incorporation of the halogen component and thedistribution of the metallic component. In addition, it is generallypreferred to impregnate the carrier material after it has been calcinedin order to minimize the risk of washing away the valuable platinumcompounds; however, in some cases, it may be advantageous to impregnatethe carrier material when it is in a gelled state.

Yet another essential ingredient of the catalyst of the presentinvention is the uniformly dispersed Group IVA metal component. Thiscomponent may be present as an elemental metal, as a chemical compoundsuch as the oxide, sulfide, halide, oxychloride, etc., or as a physicalor chemical combination with the porous carrier material and/or othercomponents of the catalytic composite. Of the Group IVA metals, the mostpreferred are germanium, lead, and tin. The Group IVA metal component ispreferably utilized in an amount sufficient to result in a finalcatalytic composite containing 0.01 to about 5 wt. % Group IVA metal,calculated on an elemental basis, with best results obtained at a levelof about 0.1 to about 2 wt. %. The Group IVA metal component may beincorporated in the catalytic composite in any suitable manner toachieve a uniform dispersion such as by coprecipitation or cogelationwith the porous carrier material, ion-exchange with the carrier materialor impregnation of the carrier material at any stage in the preparation.It is to be noted that it is intended to include within the scope of thepresent invention all conventional methods for incorporating a metalliccomponent in a catalytic composite. One preferred method ofincorporating the Group IVA metal component into the catalytic compositeinvolves coprecipitating the metal component during the preparation ofthe preferred refractory oxide carrier material. In the preferred case,this involves the addition of suitable soluble Group IVA metal compoundssuch as stannous or stannic halide, germanium tetrachloride, leadnitrate, etc. to the alumina hydrosol, and then combining the hydrosolwith a suitable gelling agent and dropping the resulting mixture into anoil bath, etc., as explained in detail hereinbefore. Following thecalcination step, there is obtained a carrier material having a uniformdispersion of a Group IVA metal oxide in an intimate combination withalumina. Another preferred method of incorporating the Group IVA metalcomponent into the catalyst composite involves the utilization of asoluble, decomposable compound of a Group IVA metal to impregnate anduniformly disperse the Group IVA metal throughout the porous carriermaterial.

Thus, the Group IVA metal component may be added to the carrier materialby commingling the latter with an aqueous solution of a suitable GroupIVA metal salt or soluble compound of Group IVA metal such as stannousbromide, stannous chloride, stannic chloride, stannic chloridepentahydrate; or germanium oxide, germanium tetraethoxide, germaniumtetrachloride; or lead nitrate, lead acetate, lead chlorate and the likecompounds. The utilization of Group IVA metal chloride compounds, suchas germanium tetrachloride or lead chlorate is particularly preferredsince it facilitates the incorporation of both the Group IVA metalcomponent and at least a minor amount of the preferred halogen componentin a single step. In general, the Group IVA metal component can beimpregnated either prior to, simultaneously with, or after the othercomponents are added to the carrier material.

Yet another essential feature of the present invention is asurface-impregnated metal component selected from the group consistingof rhodium, ruthenium, cobalt, nickel, or iridium. As heretofore noted,while the prior art has recognized that a platinum-Group IVA metalreforming catalyst may advantageously contain a third metal component,it was believed essential that this metal component be uniformlydistributed throughout the catalyst to achieve beneficial results. Byway of contrast, it has now been determined that improved performancemay be achieved by incorporating a surface-impregnated metal componentinto a reforming catalyst composite containing uniformly dispersedplatinum and Group IVA metal as opposed to the uniformly distributedmetal component of the art. It is to be understood that as utilizedherein, the term "surface-impregnated" means that at least 80% of thesurface-impregnated component is located within the exterior surface ofthe catalyst particle. The term "exterior surface" is defined as theoutermost layer of the catalyst, preferably that which comprises theexterior 50% of the catalyst volume. Expressed in an alternative way,the term "exterior surface" is defined as the exterior 0.2r layer whenthe catalyst is spherical in shape and 0.3r when the catalyst iscylindrical in shape and the length to diameter ratio of the cylinder isgreater than or equal to 2:1. In both of these formulae, "r" is definedas the nominal radius of the support. However, when the shape of thecatalyst is such that the determination of the radius is ambiguous(e.g., a cloverleaf shape), then the "exterior surface" is defined asthe outermost layer of the catalyst comprising the exterior 50% of thecatalyst volume. By "layer", it is meant a stratum of substantiallyuniform thickness.

A metal component is considered surface-impregnated when the averageconcentration of said metal component within the exterior surface of thecatalyst is at least 4 times the average concentration of the same metalcomponent in the remaining interior portion of the catalyst.Alternatively, a metal component is said to be surface-impregnated whenthe average atomic ratio of the metal component to the uniformlydispersed platinum component is at least 4 times greater in magnitudewithin the exterior surface of the catalyst than it is within theremaining interior portion.

As previously stated, the surface-impregnated metal is selected from thegroup consisting of rhodium, ruthenium, cobalt, nickel or iridium. Thesurface-impregnated metal component may be present in the composite asan elemental metal or in chemical combination with one or more of theother ingredients of the composite, or as a chemical compound of themetal such as the oxide, oxyhalide, sulfide, halide, and the like. Themetal component may be utilized in the composite in any amount which iscatalytically effective, with the preferred amount being about 0.01 toabout 2 wt. % thereof, calculated on an elemental metal basis.Typically, best results are obtained with about 0.05 to about 1 wt. % ofthe surface-impregnated metal. Additionally, it is within the scope ofthe present invention that beneficial results may be obtained by havingmore than one of the above-named metals surface-impregnated on thecatalyst.

The surface-impregnated component may be incorporated into the catalyticcomposite in any suitable manner which results in the metal componentbeing concentrated in the exterior surface of the catalyst support inthe preferred manner. In addition, it may be added at any stage of thepreparation of the composite--either during preparation of the carriermaterial or thereafter--and the precise method of incorporation used isnot deemed to be critical so long as the resulting metal component issurface-impregnated as the term is used herein. A preferred way ofincorporating this component is an impregnation step wherein the porouscarrier material containing uniformly dispersed Group IVA metal andplatinum is impregnated that no "additional" acid compounds are to beadded to the impregnation solution. In a particularly preferred methodof preparation, the carrier material, containing Group IVA metal andplatinum, is subjected to oxidation and halogen stripping procedures, asis explained hereinafter, prior to the impregnation of thesurface-impregnated metal components. Aqueous solutions of watersoluble, decomposable surface-impregnated metal compounds are preferred,including hexaminehodium chloride, rhodium carbonylchloride, rhodiumtrichloride hydrate, ammonium pentachloroaquoruthenate, rutheniumtrichloride, nickel chloride, nickel nitrate, cobaltous chloride,cobaltous nitrate, iridium trichloride, iridium tetrachloride and thelike compounds.

The catalyst composite of the instant invention is considered by thoseskilled in the art to be an acidic catalyst. Accordingly, it isessential that the catalyst contain a halogen component which imparts tothe composite the necessary acidic function. As hereinabove mentioned,it is preferred that the carrier material containing platinum and GroupIVA metal be subjected to oxidation and halogen stripping proceduresprior to addition of the surface-impregnated metal component. Thepresence of excessive amounts of halogen or halide, for example,chloride, on the carrier prior to the addition of thesurface-impregnated metal, will prevent attainment of the novel surfacedeposited feature of the instant invention. The oxidation can be carriedout at temperatures from about 93° to about 593° C. in an air atmospherefor a period of about 0.5 to about 10 hours in order to convert themetallic components substantially to the oxide form. The strippingprocedure is conducted at a temperature of from about 371° to about 593°C. in a flowing air/steam atmosphere for a period of from about 1 to 10hours. Following addition of the surface-impregnated metal component,the halogen is then added under oxidative conditions to the carriermaterial. Although the precise form of the chemistry of the associationof the halogen component with the carrier material is not entirelyknown, it is customary in the art to refer to the halogen component asbeing combined with the carrier material, or with the other ingredientsof the catalyst in the form of the halide (e.g., as the chloride). Thiscombined halogen may be fluoride, chloride, iodide, bromide, or mixturesthereof. Of these, fluoride and, particularly, chloride are preferredfor the purposes of the present invention. The halogen may be added tothe carrier material in any suitable manner after the addition of thesurface-impregnated metal component. For example, the halogen may beadded as an aqueous solution of a suitable decomposablehalogen-containing compound such as hydrogen fluoride, hydrogenchloride, hydrogen bromide, ammonium chloride, etc. For reforming, thehalogen will be typically combined with the carrier material in anamount sufficient to result in a final composite that contains about 0.1to about 3.5 wt. % and preferably about 0.5 to about 1.5 wt. % ofhalogen calculated on an elemental basis.

Another significant parameter for the present catalyst is the "totalmetals content" which is defined to be the sum of the platinumcomponent, Group IVA metal component and the surface-impregnated metalcomponent, calculated on an elemental basis. Good results are ordinarilyobtained with the subject catalyst when this parameter is fixed at avalue of about 0.2 to about 6 wt. %, with best results ordinarilyachieved at a metals loading of about 0.3 to about 2 wt. %.

Regardless of the details of how the components of the catalyst arecombined with the porous carrier material, the final catalyst generallywill be dried at a temperature of about 93° to about 316° C. for aperiod of from about 2 to about 24 hours or more, and finally calcinedor oxidized at a temperature of about 371° to about 593° C. in an airatmosphere for a period of about 0.5 to about 10 hours in order toconvert the metallic components substantially to the oxide form. Bestresults are generally obtained when the halogen content of the catalystis adjusted during the calcination step by including water and a halogenor a decomposable halogen-containing compound in the air atmosphereutilized. In particular, when the halogen component of the catalyst ischlorine, it is preferred to use a mole ratio of H₂ O to HCl of about5:1 to about 100:1 during at least a portion of the calcination step inorder to adjust the final chlorine content of the catalyst to a range ofabout 0.5 to about 1.5 wt. %.

It is preferred that the resultant calcined catalytic composite besubjected to a substantially water-free reduction step prior to its usein the conversion of hydrocarbons. This step is designed to ensure auniform and finely divided dispersion of the platinum componentthroughout the carrier material. Preferably, substantially pure and dryhydrogen (i.e., less than 20 vol. ppm H₂ O) is used in the reducingagent in this step. The reducing agent is contacted with the calcinedcatalyst at a temperature of about 427° to about 649° C. and for aperiod of time of about 0.5 to 10 hours or more, effective to reducesubstantially all of the platinum component and the surface-impregnatedmetal component to the elemental state. However, in the case where thesurface-impregnated metal component is nickel or cobalt, then thesurface-impregnated metal may be primarily in the oxide form after thereduction step. This reduction treatment may be performed in situ aspart of a startup sequence if precautions are taken to predry the plantto a substantially water-free state and if substantially water-freehydrogen is used.

The resulting reduced catalytic composite may, in some cases, bebeneficially subjected to a presulfiding operation designed toincorporate in the catalytic composite from about 0.05 to about 0.50 wt.% sulfur calculated on an elemental basis. Preferably, this presulfidingtreatment takes place in the presence of hydrogen and a suitablesulfur-containing compound such as hydrogen sulfide, lower molecularweight mercaptans, organic sulfides, etc. Typically, this procedurecomprises treating the reduced catalyst with a sulfiding gas such as amixture of hydrogen and hydrogen sulfide having about 10 moles ofhydrogen per mole of hydrogen sulfide at conditions sufficient to effectthe desired incorporation of sulfur, generally including a temperatureranging from about 10° up to about 593° C. or more. It is generally agood practice to perform this presulfiding step operation undersubstantially water-free conditions.

EXAMPLES

The following working examples are given to illustrate further theutility of the catalytic composite of the present invention in thereforming of naphtha. It is understood that the examples are intended tobe illustrative rather than restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical depiction of Catalyst A, made in accordance withthe invention, comparing the distribution profiles of platinum and tinbeing uniformly dispersed to rhodium being nonuniformly dispersedthrough the catalyst particle of the present invention.

FIG. 2 is a graphical depiction of Catalyst B, not of the instantinvention, showing the distribution profiles of platinum, tin andrhodium, all being uniformly dispersed through a catalyst particle ofthe prior art.

FIG. 3 is a graphical depiction of catalyst selectivity as measured bythe C₅ ⁺ reformate volume percent yield as a function of catalyst lifemeasured in barrels of charge stock processed per pound of catalyst.Performance data for both Catalyst A and Catalyst B are shown.

FIG. 4 is a graphical depiction of catalyst activity as measured byaverage reaction zone temperature necessary to provide a reformate of102 research octane number as a function of catalyst life measured inbarrels of charge stock processed per pound of catalyst. Again,performance data for both Catalyst A and Catalyst B are shown.

EXAMPLE I

This example sets forth a preferred method of preparing the catalyticcomposite of the present invention. A tin-containing alumina sphere wasprepared by cogelling an alumina hydrosol containing a soluble compoundof tn by oil-drop method. After oil-dropping and aging, the cogelledspheres were dried and calcined. The resulting particles compriseduniformly distributed tin oxide and alumina in the shape of sphereshaving an approximate diameter of 1500 microns.

An aqueous impregnation solution containing chloroplatinic acid andhydrogen chloride was then prepared. This solution contained hydrogenchloride in an amount corresponding to about 2 wt. % of the carriermaterial to be impregnated. The amount of hydrogen chloride utilized inthe impregnation solution was selected to assure good dispersion ofplatinum throughout the catalyst particle.

The amount of platinum component in the impregnation solution utilizedto make the catalyst of the present invention was sufficient to resultin a finished catalyst composite containing 0.375 wt. % platinum. Afterimpregnation, the catalyst was dried and calcined. After calcination,the catalyst was subjected to a chloride stripping procedure to removeany excess chloride ions that would have a deleterious effect on thesubsequent rhodium impregnation. As heretofore mentioned, the presenceof excess chloride ions would cause the rhodium to be uniformlydistributed throughout the carrier material and not remain in theexternal 300 micron layer as is essential in the instant invention. Thestripping procedure was conducted at a temperature of about 527° C. bypassing a flowing air/stream mixture across the catalyst composite forapproximately 2 hours.

The resulting composite was next contacted with a rhodium-containingaqueous solution prepared by adding rhodium trichloride hydrate to waterin an amount sufficient to result in a composite containing 0.05 wt. %rhodium.

After the rhodium impregnation, the catalyst was again dried andcalcined. After calcination the catalyst was subjected to a chlorinationstep to add the halogen component. After chlorination, the catalyst wasreduced in a dry hydrogen stream for about 1 hour.

The resulting catalyst particles were analyzed and found to contain, onan elemental basis, about 0.375 wt. % platinum, about 0.05 wt. %rhodium, about 0.3 wt. % tin and about 1.05 wt. % chlorine. Thiscatalyst was designated Catalyst A. In order to determine whether therhodium component was surface-impregnated Catalyst A was subjected to anelectron microprobe distribution analysis. The results of this analysisas set forth in FIG. 1. As can be noted, FIG. 1 is a normalized ratio ofrhodium to aluminum as a function of the distance from the sphere edgein microns. The graph indicates that there is no rhodium beyond a depthof about 150 microns from the sphere edge. Accordingly, it can be seenthat Catalyst A comprises a surface-impregnated rhodium component.

EXAMPLE II

In this example, a catalyst was made in a fashion such that the rhodiumcomponent was uniformly dispersed throughout the catalyst particle. Theresulting catalyst represents the catalyst compositions of the priorart. The important differences between the procedures used to make theprior art catalyst and Catalyst A are that the prior art procedureutilizes a co-impregnation of platinum and rhodium and does not employ achloride stripping procedure. Accordingly, the catalyst of this examplewas prepared by starting with the same tin-containing alumina as inCatalyst A. A sulfur-free aqueous solution containing chloroplatinicacid, rhodium trichloride hydrate, and hydrogen chloride was thenprepared. Similarly, this solution contained hydrogen chloride in anamount corresponding to about 2 wt. % of the carrier material to beimpregnated. The amount of metallic components in the impregnationsolution utilized to make the catalyst was sufficient to result in afinal composite containing 0.375 wt. % platinum and 0.05 wt. % rhodium.After impregnation, the catalyst was dried and calcined in the samemanner as Catalyst A. After calcination, the catalyst was similarlysubjected to a chlorination step to add the halogen component. Afterchlorination, the catalyst was reduced in a dry hydrogen stream forabout 1 hour. The final catalyst composite comprised, on an elementalbasis, about 0.375 wt. % platinum, about 0.05 wt. % rhodium, about 0.3wt. % tin, and about 1.05 wt. % chlorine. This catalyst was designatedCatalyst B.

In order to determine the rhodium distribution in Catalyst B, Catalyst Bwas subjected to an electron microprobe distribution analysis. Theresults of this analysis are set forth in FIG. 2. FIG. 2 is a graph ofthe ratio of the counts of rhodium at a given distance from the sphereedge divided by the counts of aluminum detected by the microprobe scan.The data in FIG. 2 clearly reveals that substantial amounts of rhodiumare dispersed in the catalyst at a depth greater than 150 microns, and,in fact, rhodium is uniformly dispersed throughout the catalyst.Accordingly, the rhodium component of Catalyst B is notsurface-impregnated.

EXAMPLE III

In order to compare Catalyst A, a composite made in accordance with theinvention, with Catalyst B, a catalyst not having a surface-impregnatedrhodium component, both catalysts were separately subjected to a highstress evaluation test designed to determine the relative activity andselectivity for the reforming of a gasoline charge stock. In all tests,the same charge stock was utilized, its characteristics are given inTable I below.

                  TABLE I                                                         ______________________________________                                        PROPERTIES OF PLATEAU UINTA                                                   BASIN NAPHTHA                                                                 ______________________________________                                        IBP, °C. 80                                                            50%             121                                                           EP              199                                                           Paraffins, vol. %                                                                             66                                                            Naphthenes, vol. %                                                                            24                                                            Olefins, vol. % --                                                            Aromatics, vol. %                                                                             10                                                            API             58.7                                                          Sulfur          <0.5 wt. ppm                                                  H.sub.2 O       10 wt. ppm                                                    Cl              1 wt. ppm                                                     Nitrogen        <13 wt. ppm                                                   ______________________________________                                    

The tests were performed in a laboratory scale reforming plantcomprising a reactor containing a catalyst undergoing evaluation, ahydrogen separating zone, a debutanizer column, suitable heating,pumping, and condensing means, etc.

In this plant, a hydrogen recycle stream and a charge stock arecommingled and heated to the desired conversion temperature. Theresulting mixture is then passed downflow into a reactor containing thecatalyst being tested as a fixed bed. An effluent stream is thenwithdrawn from the bottom of the reactor, cooled to about 0° C. andpassed to the separating zone wherein a hydrogen-rich gaseous phaseseparates from a liquid phase. The hydrogen-rich gaseous phase is thenwithdrawn from the separating zone and a portion of it is continuallypassed through a high surface area sodium scrubber. The resultingsubstantially water-free hydrogen stream is then recycled to the reactorin order to supply hydrogen for the reaction. The excess hydrogen overthat needed for recycle is recovered as excess separator gas. Moreover,the liquid phase from the separating zone is withdrawn therefrom andpassed to the debutanizer column wherein light ends are taken overheadas debutanizer gas and a C₅ ⁺ reformate stream recovered as bottoms.

The conditions utilized in both tests were a reaction zone outletpressure of about 345 kPa (ga), a 5.0 molar ratio of hydrogen-rich vaporto hydrocarbon charge stock, and a 2.0 liquid hourly space velocity.Reaction zone temperatures were selected to achieve a hydrocarbonproduct reformate of 102 research octane number. The results of testingof Catalysts A and B are set forth in FIGS. 3 and 4.

FIG. 3 is a graphical depiction of the C₅ ⁺ liquid volume percent yield,based on the volume of hydrocarbon charge stock, as a function ofcatalyst life as measured by the barrels of charge stock processed perpound of catalyst. Surprisingly and unexpectedly, Catalyst A, containinga surface-impregnated rhodium component consistently exhibits a higherC₅ ⁺ liquid volume percent yield of 102 research octane numberreformate. Accordingly, Catalyst A exhibits improved selectivity for theproduction of 102 research octane number reformate relative to CatalystB. FIG. 4 is a graphical depiction of the average reactor inlettemperature necessary to achieve a reformate of 102 research octanenumber as a function of catalyst life defined as barrels of charge stockprocessed per pound of catalyst. Using the average inlet temperature asa measure of catalyst activity, it can be seen that surprisingly andunexpectedly Catalyst A, having a surface-impregnated rhodium component,exhibits a higher activity (lower average reactor inlet temperature)than is exhibited by Catalyst B. More importantly, Catalyst A exhibitsgreater activity stability as measured by the slope of the averagereactor inlet temperature line. Thus, comparing the performance of thetwo catalysts at a given end-of-run temperature, for example, 532° C.,shows that Catalyst A processed 124% more charge stock than did CatalystB. In other words, Catalyst A had more than twice the stability as thatof Catalyst B. Accordingly, Catalyst B showed much greater loss ofactivity as measured by the respective slopes of the inlet temperaturelifelines.

EXAMPLE IV

The catalyst described in this example represents another catalystcomposite of the present invention. An oxidized, chloride-strippedspherical catalyst particle containing platinum and tin uniformlydispersed on an alumina support was prepared by following the procedureoutlined in Example 1. An impregnation solution containing ammoniumpentachloroaquoruthenate and water was contacted with the platinum andtin containing spherical particles in a manner to result in a compositecontaining 0.5 wt. % surface-impregnated ruthenium. After the rutheniumimpregnation, the catalyst was dried and calcined. After calcination,the composite was subjected to a chlorination step to add the halogencomponent. After chlorination, the catalyst was reduced in a dryhydrogen stream for about 1 hour.

The resulting catalyst particles were found to contain, on an elementalbasis, about 0.375 wt. % uniformly dispersed platinum, about 0.5 wt. %surface-impregnated ruthenium, about 0.3 wt. % uniformly dispersed tinand about 1.05 wt. % chlorine. This catalyst was designated as CatalystC.

EXAMPLE V

To illustrate clearly the benefits of surface-impregnated ruthenium, acatalyst composite with uniformly dispersed ruthenium was prepared forcomparison. In making this uniformly dispersed ruthenium-containingcatalyst, a uniformly dispersed tin containing alumina support,identical to that used for preparing Catalyst C was contacted with animpregnation solution containing chloroplatinic acid, rutheniumtrichloride, and 12 wt. % hydrogen chloride based on the weight of thecarrier material. This high acid solution was selected to assure auniform dispersion of both the platinum and ruthenium. The drying,calcining, and halogen addition steps were identical to that used forCatalyst C. Accordingly, this catalyst was made in accordance with theteachings of U.S. Patent 3,909,394. The final catalyst compositecomprised, on an elemental basis, about 0.375 wt. % uniformly dispersedplatinum, about 0.5 wt. % uniformly dispersed ruthenium, about 0.3 wt. %uniformly dispersed tin, and about 1.05 wt. % chlorine. This catalystwas designated Catalyst D.

EXAMPLE VI

In order to compare Catalyst C, a composite made in acordance with theinvention was Catalyst D, a catalyst not having a surface-impregnatedmetal component, both catalysts were tested following the procedureoutlined in Example III.

The performance results are presented in Table II. It is observed that,at the completion of a 25° C. temperature cycle, Catalyst C producesslightly higher C₅ ⁺ liquid volume percent yield of 102 research octanenumber reformate than does the uniformly dispersed ruthenium catalyst.More importantly, Catalyst C, having surface-impregnated ruthenium, ismuch more activity stable as evidenced by the lower ratio of temperatureto barrles of feed processed per pound of catalyst loaded and is capableof processing about 30% more feed than Catalyst B for the sametemperature cycle. In other words, the uniformly dispersed rutheniumcatalyst, Catalyst D, deactivated about 35% faster than the catalystcomposite of the instant invention.

                  TABLE II                                                        ______________________________________                                        Catalyst             C        D                                               ______________________________________                                        Ru Impregnation      Surface  Uniform                                         Start-of-run temp. @ 0.3 BPP, °F.                                                           960      964                                             Avg. C.sub.5 + liq. vol. % yield                                                                   79.3     79.1                                            Deactivation Rate, °F./BPP                                                                  35.7     48.4                                            ______________________________________                                    

EXAMPLE VII

The catalyst described in this example represents another catalystcomposite of the instant invention. An oxidized, chloride-strippedspherical catalyst particle containing platinum and tin uniformlydispersed on an alumina support was prepared following the procedureoutlined in Example 1. An impregnation solution containing nickelnitrate and isopropanol was contacted with the platinum and tincontaining spherical particles in a manner to result in a compositecontaining 0.36 wt. % surface-impregnated nickel. After the nickelimpregnation, the catalyst was dried and calcined. After calcination,the catalyst was subjected to a chlorination step to add the halogencomponent. After chlorination, the catalyst was reduced in a dryhydrogen stream for about 1 hour.

The resulting catalyst particles were found to contain 0.387 wt. %uniformly dispersed platinum, 0.36 wt. % surface-impregnated nickel, 0.3wt. % uniformly dispersed tin and 1.05 wt. % chlorine. This catalyst wasdesignated as Catalyst E.

EXAMPLE VIII

To illustrate the advantages of having surface-impregnated nickel, acatalyst composite was prepared for comparison wherein the nickel wasuniformly dispersed throughout the catalyst composite. In preparation ofthe uniformly dispersed nickel containing catalyst, a uniformlydispersed tin containing alumina support, identical to that used forpreparing Catalyst E, was contacted with an impregnation solutioncontaining chloroplatinic acid, nickel nitrate, and 2 wt. % hydrogenchloride based on the weight of the alumina carrier material. Thishydrogen chloride level was selected to allow for uniform dispersion ofboth the platinum and nickel metals. The drying, calcining, and halogenaddition steps were identical to that used for Catalyst E. The finalcatalyst composite comprised, on an elemental basis, 0.39 wt. %uniformly dispersed platinum, 0.36 wt. % uniformly dispersed nickel, 0.3wt. % uniformly dispersed tin, and 1.14 wt. % chlorine. This catalystwas designated Catalyst F.

EXAMPLE IX

The catalyst described in this example represents another catalystcomposite of the instant invention. An oxidized, chloride-strippedspherical catalyst particle containing platinum and tin uniformlydispersed on an alumina support was prepared following the procedureoutlined in Example I. An impregnation solution containing cobaltouschloride and isopropanol was contacted with the platinum and tincontaining spherical particles in a manner to result in a compositecontaining 0.42 wt. % surface-impregnated cobalt. After the cobaltimpregnation, the catalyst was subjected to the identical finishingconditions as those used in Example VII.

The resulting catalyst particles were found to contain 0.384 wt. %uniformly dispersed platinum, 0.42 wt. % surface-impregnated cobalt, 0.3wt. % uniformly dispersed tin and 1.03 wt. % chlorine. This catalyst wasdesignated Catalyst G.

EXAMPLE X

Catalysts E, F, and G were performance tested in the identical manner asset forth in Example III. Tables III and IV present the results.Comparing Catalyst E to Catlyst F, as listed in Table III, shows thatthe surface-impregnated nickel catalyst surprisingly and unexpectedlyexhibited an average 1.1 percent greater C₅ ⁺ liquid volume yield of 102research octane number reformate compared to Catalyst F having uniformlydispersed nickel. More importantly, the surface-impregnated catalystdeactivates at a much lower rate than the uniformly dispersed nickelcatalyst, resulting in an activity stability improvement of 48%. Thisstability improvement allows for 56% more feedstock to be processed in agiven 17° C. temperature cycle by the catalyst of the instant inventioncompared to the uniformly dispersed nickel containing catalyst.

Test results for Catalyst G, shown in Table IV, similarly illustrateexceptional performance, thus demonstrating the surprising benefitrealized when surface-impregnated cobalt is employed with uniformlydispersed platinum and tin.

                  TABLE III                                                       ______________________________________                                        Catalyst             E        F                                               ______________________________________                                        Ni Impregnation      Surface  Uniform                                         Start-of-run temp. @ 0.3 BPP, °F.                                                           955      958                                             Avg. C.sub.5 + liq. vol. % yield                                                                   80.4     79.3                                            Deactivation Rate, °F./BPP                                                                  28.5     42.9                                            ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                        Catalyst              G                                                       ______________________________________                                        Co Impregnation       Surface                                                 Start-of-run temp. @ 0.3 BPP, °F.                                                            948                                                     Avg. C.sub.5 + liq. vol. % yield                                                                    80.6                                                    Deactivation Rate, °F./BPP                                                                   17.6                                                    ______________________________________                                    

EXAMPLE XI

This example presents data for a catalyst composite of the instantinvention wherein platinum and germanium are uniformly dispersedthroughout the composite and ruthenium is surface-impregnated. Thiscatalyst was designated as Catalyst H and contained 0.375 wt. %platinum, 0.25 wt. % germanium, and 0.5 wt. % of surface-impregnatedruthenium.

Catalyst H was prepared by impregnating a spherical alumina support,prepared by the oil drop method, with platinum, germanium, and rutheniumin an aqueous solution containing 2 wt. % hydrochloric acid, based onthe weight of the alumina support. The impregnated composite wassubjected to the same oxidation and reduction procedures as thosedescribed in Example VII.

Catalyst H was evaluated in a pilot plant test following the same testprocedure as described in Example III. Test results are presented inTable V.

                  TABLE V                                                         ______________________________________                                        Catalyst              H                                                       ______________________________________                                        Ru Impregnation       Surface                                                 Start-of-run temp. @ 0.3 BPP, °F.                                                            965                                                     Avg. C.sub.5 + liq. vol. % yield                                                                    79.8                                                    Deactivation Rate, °F./BPP                                                                   64                                                      ______________________________________                                    

EXAMPLE XII

This example presents a method of preparing a catalyst of the instantinvention comprising uniformly dispersed platinum, uniformly dispersedlead, and surface-deposited rhodium. The preparation procedure wouldfollow identically the procedure set forth in Example 1 except that leadnitrate would be substituted for the soluble tin compound. By adjustingthe quantities of lead nitrate, chloroplatinic acid, and rhodiumtrichloride, a catalyst could be prepared containing about 0.38 wt. %platinum, 0.05 wt. % rhodium, about 0.3 wt. % lead, and about 1.0 wt. %chlorine. This catalytic composite could adequately be employed for thereforming of hydrocarbons.

In summary, it can be seen from the above performance test results thata superior reforming process results from incorporating asurface-impregnated metal component in a reforming catalyst inaccordance with the present invention.

What is claimed is:
 1. A process for the catalytic reforming of naphthacharge stock comprising contacting the naphtha and hydrogen at reformingconditions with a catalytic composite comprising a uniformly dispersedplatinum component, a uniformly dispersed Group IVA metal component, asurface-impregnated metal component selected from the group consistingof rhodium, ruthenium, cobalt, nickel, or iridium, and a halogencomponent on a refractory support having a nominal diameter of at least650 microns.
 2. The process of claim 1 further characterized in that thehalogen component comprises a chlorine component.
 3. The process ofclaim 1 further characterized in that the reforming conditions include apressure of from about 345 to about 862 kPa (ga), a reaction temperaturein the range of from about 427 to about 593° C., a liquid hourly spacevelocity of about 0.1 to about 10 hr-1, and about 1 to about 20 moles ofhydrogen per mole of hydrocarbon entering the reforming zone.
 4. Theprocess of claim 1 further characterized in that the catalytic compositecomprises, on an elemental basis, from about 0.05 to about 1 wt. %platinum, from about 0.05 to about 1 wt. % surface-impregnated metal,from about 0.1 to about 2 wt. % Group IVA metal, and from about 0.5 toabout 1.5 wt. % chlorine on a support having a nominal diameter of about1500 microns.
 5. The process of claim 4 further characterized in thatthe Group IVA metal comprises germanium.
 6. The process of claim 4further characterized in that the Group IVA metal comprises lead.
 7. Theprocess of claim 4 further characterized in that the Group IVA metalcomprises tin.